The invention relates generally to the field of laser marking systems. More particularly, the invention concerns an apparatus that uses laser energy for marking indicia on photosensitive web with a dramatic reduction in the occurrence of fog on the photosensitive web.
Conventional edge marking in photographic film manufacturing involves printing some sort of identification indicia along the edge of film rolls during the finishing operation. Edge marked film has direct verification of roll identity, sheet identity and waste identity during all stages of the manufacturing process. Importantly, edge marked film provides accurate footage identification that enables operators to quickly identify, trace and remove film imperfections, thereby minimizing the amount of product waste. More generally, edge marked film increases process understanding by allowing process interactions to be more closely identified with their corresponding effect on the product. Traditional embossing marking techniques are being replaced by laser edge marking. Current mechanical embossing techniques (embossing wheels) are not programmable, generate poor quality marks and require excessive maintenance. Laser edge marking, on the other hand, is particularly advantageous in the industry because it provides a permanent record and can be read before and after film processing.
Advances in laser technology enabled the use of a dot matrix CO2 laser marking system to be used to replace existing embossing technology. Off the shelf laser marking equipment will mark the film at required throughput rate, however, an unacceptable level of fog spots occurred.
Thus, a particular shortcoming of these advanced high powered laser systems used for edge marking photosensitive film is that they produce a by-product that impinges on the film surface. Laser energy by-products in the form of a plume of energized smoke and irradiated debris on the film surface is known to cause the localized fogging on the film. Experience has shown that localized fogging is not easily eliminated even when the film is immersed in a 99.8% nitrogen atmosphere.
More recent developments in laser technology enabled the development of high speed marking systems using short pulse lasers. Short pulse laser exposure on photosensitive film shows some promise in reducing the occurrences of fog spots. Our experience also indicates that an air jet directed at the laser impingement point on the film surface further reduce the occurrence of fog. Statistical methods have been employed to gain information on fog incidence reduction when laser marking photosensitive film. It has been experimentally proven that laser pulse width does not have a significant effect on fog. Importantly, however, our experience does suggest that laser peak power has a dramatic effect on the reduction of occurrences of fog spots by a factor of about 30. In addition, significant statistical benefits can be derived from an air jet that we believe can further reduce the incidences of fog spots by a factor of about 10.
Hence, laser marking without controlling peak power will result in 14% to 50% of the laser-generated dots of dot matrix characters to have fog spots around the dots. There are no present attempts known to the inventors to control peak power in laser edge marking devices because embossing techniques still remain prevalent in the industry and, more importantly, the fog spots remain a significant quality issue during the finishing process.
Therefore, a need persists for variable information to be permanently marked on die edge of each sheet of photosensitive web, such as photographic film, without significant incidences of fog spots on the surface of the film.
It is, therefore, an object of die invention to provide an apparatus for laser marking indicia on a moving photosensitive web while substantially reducing the occurrence of deleterious fog spots on the photosensitive web.
It is another object of the invention to provide an apparatus for exposing a moving photosensitive web to laser energy while controlling the peak power of the laser energy.
Yet another object of the invention is to provide an apparatus for laser printing indicia on a photosensitive web by further directing a jet of air onto the laser energy impinged surface of the photosensitive web.
It is a feature of the invention that the apparatus for laser marking indicia on a moving photosensitive web has a nozzle element for reducing the incident of fog spots on the laser impinged photosensitive web.
To accomplish these and other objects and features and advantages of the invention, there is provided, in one aspect of the invention, an apparatus for marking indicia on a moving photosensitive web, comprising:
a source of laser energy;
laser printer means operably connected to said source of laser energy, said laser printer means being provided with:
a laser head;
a laser beam tube connected to said laser head, said laser beam tube having an active end; and,
a nozzle element structurally associated with said active end of said laser beam tube, said nozzle element comprising a chamber having a laser energy inlet end and a laser energy outlet end; an air jet member arranged in said chamber for directing a burst of air onto a laser beam impingeable surface; at least one lens arranged in said chamber for focusing each one of a plurality of laser beams passing through said chamber; a lens cleaning member arranged in said chamber proximate to said at least one lens; and, a vacuum port extending from said chamber, said vacuum port providing means for evacuating said chamber of smoke and debris generated during laser marking; and wherein said laser head has a plurality of lasers disposed therein for generating a plurality of laser beams, a lens arranged in said laser beam tube for focusing said each one of a plurality of laser beams along a predetermined optical path through said laser beam tube and into impinging contact with said moving photosensitive web thereby producing said indicia thereon.
It is, therefore, an advantageous effect of the present invention that laser edge markings on photosensitive web can be accomplished with an apparatus that is easy to operate, simple and cost effective to produce and that substantially reduces the occurrence of fog spots on the photosensitive web.